1. Field of the Invention
The invention relates to a measuring device for the measurement of properties of a material to be measured, in particular of the moisture content of agricultural harvested products such as hay, straw, or wilted silage, with a moisture sensor element and at least one further sensor element for the detection of other material properties. The invention further relates to a method for measuring properties of a material to be measured in a measuring device.
2. Description of the Related Art
Both for the obtaining of high-quality animal feed as well as for its utilisation, such as in feed mixing vehicles, a precise knowledge of the moisture content or of the dry mass of the feed is of decisive significance. Despite decades of development work, it has not yet proved possible for a moisture-measuring device to be created for compactable stalk or stem products which will fulfill the requirements for the precision of measurement at economically viable costs.
The problem lies in the fact that, with a constant assumed mass volume of a compactable stalk or stem product (such as wilted grass), the proportions of air and water to the dry mass vary very sharply as a function of the compaction. The consequence of this is that, for example, certain measuring devices measure highly-compacted material to be measured as being too moist.
A device is also known from German patent application DE 32 32 746 A1 in which a harvesting machine is provided with a meter for determining the amount of product entering the harvesting machine. The meter comprises pivoted feelers that move in response to the through flow of product. The feelers are connected to potentiometers which determine the angular extent by which the feelers pivot. The tips of the feelers in contact with the product may also be provided with electrodes for measuring moisture content. Since the feelers are biased against the product, improved contact is thus achieved between the product and the electrode.
In order to exclude the influence of different material densities, it has also been proposed that the material be measured in a state of as constant density as possible. As a result, the measuring points in an agricultural harvesting machine and the scope of application are severely restricted, because in practice measurement can be taken only on compacted bales or at the intake point of the material into the compression chamber of a variable round bale press. Basically, however, the disadvantage pertains that a constant and continuous pressure cannot be achieved at all at the measuring point because of the fluctuating material infeed over the height and width of the infeed aperture. The consequence of this is relatively imprecise measured values of this moisture-measuring device. Devices of this type are disclosed in German patent applications DE 23 03 109 A, DE 199 59 117 A1, and DE 102 04 941 A1.
From EP 0 843 959 A1 a measuring device is known in an agricultural machine with a microwave sensor. The moisture of the stationary or moving harvested material in the machine is intended to be determined by assessment of the damping of specific frequencies. A further method for the measurement of the material moisture of a material to be measured with the aid of microwaves is known from EP 0 468 023 B1. In this situation, it is intended that a measurement of the moisture values regardless of the density should be possible by an evaluation of the microwave signals. It is intended that the displacement should be determined of the resonance frequency of a resonator, caused by the moist mass. This method is suitable for relatively homogenous materials such as tobacco, coffee, marzipan, cheese, or similar materials. Measuring devices of this kind have to date not developed beyond the experimental stage, at least with regard to bale presses for agricultural stalk or stem materials. On the one hand, these measuring devices are very expensive and fall within the range of the costs of the machine in which they are to be used, such as a round bale press. On the other, these measuring devices are designed more for laboratory operation and stationary production processes. The main reason, however, lies in the fact that the precision of measurement for very inhomogeneous stem or stalk materials such as straw, hay, grass, or clover can only be represented by precise calibrations.
Thus, there is a particular need for an improved moisture measurement device that can meet the above-mentioned requirements of accuracy and cost.